The proposed research is organized around a search for differences between normal and malignant cells in their responses to nutrient and growth-regulating factors. The requirements for growth in culture of a variety of normal and malignant cells from humans, mice, rats, rabbits, and chickens will be studied, with major emphasis on cells of epithelial morphology. The requirement for serum proteins will be minimized by adjusting all components of the defined portion of the culture medium to experimentally determined optimum concentrations, by adding growth-promoting substances such as trace elements that are missing from many common media, by modifying the culture surface, by minimizing cellular damage during trypsinization, and by careful attention to all environmental factors. Elimination of non-specific requirements for serum proteins will make it easier to isolate and characterize those factors that continue to be required by cells grown under the improved conditions. Each time the detailed requirements of a normal cell are worked out, they will be compared with those of chemically or virally transformed cells or spontaneous tumors of similar origin. The major objectives of the research are to define precisely the nutrient requirements of various normal cells, to develop improved media for use in research involving normal cells, and to identify differences between normal and malignant cells that might provide the basis for future clinical studies on the control of malignancy.